Electrical testing apparatus



May 16, 1950 s. E. FRlsBlE Erm.

ELECTRIcAL TESTING APPARATUS Filed Aug. 30, 1948 A Tram/fx Patented May 16, 1950 UNITED STATES PATENT OFFICE ELECTRICAL TESTING APPARATUS New York Application August 30, 1948, Serial N0. 46,794

6 Claims.

This invention relates to electrical testing apparatus and more particularly to automatic 1mpedance measuring apparatus.

An object of this invention is to prov1de a new and eilicient apparatus for determining electrical characteristics of articles.

In accordance with one embodiment of this invention an apparatus is provided for automatically determining whether or not a pair of separate impedance units fall within predetermined minimum and maximum impedance limits desired for each impedance unit. The apparatus is provided with an impedance detector equipped with a number of selectively connectible standards and means for sequentially comparing the impedance units under test against the standards, the output of the detector being adapted to operate and lock a separate relay for each of the following conditions if the pair of impedance units meets the following test: Impedance unit No. 1, less than maximum and more than minimum; impedance unit No. 2, less than maximum and more than minimum. The contemporaneous operation of the four relays closes a circuit to an acceptance solenoid which may be adapted to operate either an indicator or a mechanical separating device. Failure of either of the lmpedance units to pass either its minimum or maximum tests will fail to operate the particular relay associated with that condition, thereby failing to complete the circuit to the acceptance device.

A complete understanding of the invention may be'y had by referring to the following detailed description taken in conjunction with the ac-rI companying single figure drawing which diagrammatically illustrates one embodiment of the invention.

The apparatus described herein may be used to check the impedance of a single impedance unit I or two impedance units I0 and in an automatic sequence, the impedance unit or units under test being placed in a test fixture I2 which supports the impedance units and connects them with the test circuit. The object of this test is to energize the operating coil |3 of an acceptance device I4 if the impedance value of the impedance unit or units under test falls within the required maximum and minimum limits. In case an impedance unit fails the test, the operating coil I3 will remain unenergized. The acceptance device I4 may be an indicator or it may be a mechanical device for causing the separation of acceptable impedance units from unacceptable units.

In case one impedance unit I0 is being tested the operating coil I3, when energized, receives its power from a source of electrical current 20 through a closed switch 2|, closed contact 22 of relay 24, contacts 26 of a switch 30, contacts 23 of relay 25, and contacts 21 of switch 30, the relay 24 being energized when the impedance of the test unit I0 is less than the permitted maximum and the relay 25 being energized and 1o locked if the impedance of the unit I0 is more than the permissible minimum. The relays 24 and 25 are operable in response to the action of a meter relay 3| controlled by an impedance detector 32 which is responsive to the impedance of the unit I0 under test.

The impedance detector 32, which includes the meter relay 3 I, is a symmetrical circuit and comprises a pair of half-wave electronic rectiiers 33 and 34, the rectifier 33 having an anode 40 and a cathode 4| and the rectier 34 having a similar anode 42 and cathode 43. The anodes 40 and 42 are connected through an isolating transformer 44 to an oscillation generator 50 and are also connected to similar resistors '5l and 52 which are joined at 53 and form parts of two adjacent comparative branches 54 and 55 of the detector The cathodes 4l and 43 are connected to ori posite ends of a resistor 5|) having a Variable contact arm 3l which .is connected to the junction 53. A lter condenser 52 is connected between the contact arm BI and the cathode i3 at a circuit junction B3 and a similar condenser 84 is connected between the contact arm 3l and the cathode 4| at a circuit junction 55. The

output oi the detector 32 is taken at the junction points 83 and 65 and connected to the operatng coil 66 of the meter relay 3| which is adapted to close circuits at 6l or t8 through its needle armature 69 depending on the direction of the current iiow through the coil 66. A coil l0 for restoring the meter armature 69 to neutral is energized by the closing of a timing switch 1|.

As shown in the drawing a standard impedance 'I3 is connected to the branch 54 through the normally closed contacts 'I4 of a relay 80 and a condenser 8|, the standard 'I3 and the condenser 8| forming a parallel path of the branch 54. A second standard impedance 82 may be substituted for the rst standard 'I3 by operation of the relay 8|) which is energized by the closure of a timing switch 83. Operation of the relay 8l breaks the circuit at 'I4 and closes the circuit at 84. The impedance unit I0, under test. to-

gether with a condenser 90 form a parallel half of the branch 55, connection being made through closed contacts 9| and 92 of a. relay 93 which is also provided with a plurality of other contacts for the make and break of other circuit portions. Power when necessary to energize the relay 93 is applied to it by the closure of a timing switch 9|.

The operation of the timing switches 2l, 1|, 83 and 94 in a predetermined timed sequence may be effected manually or by properly timed cams |00, IBI, |02 and |03 which may be operated in any suitable known manner.

In the operation of the detector 32 the direct current voltage drop across the portion of the resistor 80 between the contact arm 5| and circuit point 53 is proportional to the impedance of the branch 52, and the direct current voltage drop across the portion of the resistor between the contact arm Si and circuit point S is proportional to the impedance oi the branch 5E). Any impedance changes in the branches .L or 5ft will be reflected in the amplitudes of the currents owing through both portions of the divided resistor 60 and since the currents ow in opposite directions, the diierentlal value (algebraic sum) will cause the meter relay ill to operate in a direction indicative of the relation between the impedance values of the branches 52 and 5d. The detector 82 being a symmetrical circuit, the standards i3 and 82 maybe of substantially the maximum and minimum impedance reference values, respectively.

In testing a single impedance unit iii the switch 3c remains closed during the entire test and the initial position of the other switches and the relays are as shown in the drawing. After the impedance unit it is connected to the xture i2, the detector 32 will respond to the value of the impedance it, and if the impedance is less than the permitted maum, the armature 69 of the meter relay Si will operate upward to close the circuit atti thereby applying power from the source to the relay l, energizing therelay, and closing its contacts 22 and itt. Closure of contacts 04 locks the relay 2&3 in an operated posi` tion. Switch li is next closed either manually or by the timed cam i @i to restore the meter relay armature Se to neutral after which switch t3 is closed either manually or by the timed cam EQ2 thereby energizing and operating the relay 8B to break the circuit at 'id and close the circuit at 84 thus substituting the minimum impedance standard 32 for the maximum standard le as part of the branch 5:3 of the detector 32. Switch li is opened at this time to release the armature SS of the meter relay Si and if the impedance of the unit I9 is more than the permitted minimuni' then the detector 32 will respond in such a manner that the armature 69 of the meter relay 3| will be operated downward to close the circuit at 68 thereby applying power from the source t@ to the relay thus to energize the relay and close its contacts 23 and l gli. Closure of the contacts ||0 locks the relay 5 in an operated position. Switch 2|- is then closed either manually or by means of the timed cam |90. thereby completing a circuit from the source oi power 20 to the operating coil I3 of the acceptance device ill. This, of course, energizes the coil I3 and operates the device I4 thus indicating that the impedance unit I0 has passed its test in that the value of its impedance was within the permitted minimum and maximum limits. After the test is completed, switch 1I is momentarily closed anda switch momentarily opened, either manually or by their associated timed cams I0! and ll2, respectively, to reset the meter relay 3l and the relays 24 and 25 to normal. If the unit under test fails either the maximum or the minimum tests, the meter relay 3| will not operate in the right direction, resulting in the failure of either relay 24 or 25 to operate and therefore maintaining an open circuit at contacts 22 or 23. Because of this, the operating coil i3 could not be energized after the timing switch 2| is closed.

In the manufacture of certain types of networks for communications apparatus it is often convenient to mount one separate impedance unit in a single can, for example, impedance units i6 and il in a can H3. A pair of such units may be tested in automatic sequence for minimum and maximum impedance limts by connecting them, as shown in the drawing, to the test fixture i2 in this test. The initial position of all the switches and relays is as shown in the drawing.

As in the previous test, if the impedance unit it falls within the prescribed limits, the relays 2t and 25 will be sequentially energized and locked. The timing switch 963 is then closed to energize and operate the relay 93 to open the contacts at 26, 821i, @i and 92 and close the circuit at con tacts E22, H23, E25 and E25. It will be seen that the break at ci and @2 and the make at H26 and E25 substitutes the impedance unit il in place of the impedance unit l@ as pari; of the branch 55 of the detector 32. In the meantime the switch t3 is opened either manually or by the passing of the cam m2 to release the relay t@ in order to again connect the maximum standard i3 into the detector circuit. Switch li is then opened to release the armature t9, and if the impedance oiI the unit ii is below the permitted maximum, the armature J9 of the meter relay Si will operate upward and close the circuit at @l thereby conducting operating current from the source 2li to a relay i3@ -to close its contacts @Si and E32. The relay i3@ is locked in operated position through the circuit at contacts 32, and the closure of contacts itil adds another link in the circuit from the power source 2t to the operating coil i3.

The meter relay armature t@ is next restored to neutral by closing the switch ll, and the minimum impedance standard B2 is substituted for the maximum standard i3 in the detector 32 by closing switch t3. If the impedance of the unit i i is above the permitted minimum, the detector 32 will respond to operate the meter relay armature 69 downward and close the circuitat et to add a further link in the circuit from the power source 253 to the operating coil i3, which circuit is next completed by the closing of the switch 2l thereby energizing the coil i3.. The path from the power source 2@ to the coil i3 includes the meter relay armature te, contacts t8, 23, 23, itl and ,22 and the switch 2i. To clear the setfor the next units to be tested, switchli is momentarily closed and switch i Ii momentarily opened to restore the relaysi, 2li, i3@ and 25 to normal,

.and switches ed and 83 areopened to restore the relays B and 93 to normal. Again as in the previously described tests, if either of the impendance units l@ orl il had failed in-either of its tests, one or more relays would fail to operate properly, resulting in open links in the power circuit from the source 2li to the operating coil i3, thus preventing its energization.

yIt is often the practice in the manufacture of impedance units having diierent values. to

5 mount them in similar containers without external markings to identify them. With this apparatus it is possible to separate a mixed batch oi' high and low value impedance units by setting up the apparatus to accept units having an impedance lower thanI a predetermined maximum. In order to test single units I0 for less than maximum impedance, the switch 30 and a switch |40 are closed for the duration of the test and the initial positions oi the other switches and relays are those shown on the drawing. Ii the unit under test is less than maximum, the meter relay armature 60 will operate upward and close the circuit at 61 to conduct operating current from the power source 20 to the relay 24, thereby closing the contacts 22 and |04 of the relay. The relay 24 is locked by the closure of contacts |04, and the closure oi.' contacts 22 completes the circuit from one side of the power source 20 to the upper end of the operating coil I3 through switch |40 and contacts 26 and 22. The powercircuit is completed by the closing of switch 2|. As in the previously described tests the circuit is restored to normal by momentarily opening switch II l and closing switch 1I.

If the impedance unit I under test had been more than maximum, the operating coil |3 would have remained unenergized, thus distinguishing such a unit as having more than the predetermined maximum impedance.

In order to distinguish between double units in single containers having lower than a predetermined maximum impedance from those having an impedance higher than the maximum, switch 301 is opened and switch |40 is closed during the test. The initial position of the other switches and the relays are those shown in the drawing. After a double unit II3 having impedance elements |0 and II is connected as shown in the drawing, the meter relay armature 60 will operate upward and close the circuit at G'I if the impedance of the element I0 is less than the maximum. The circuit through 61 conducts operating current from the power source 20 to the relay 24, thus closing the contacts 22 and |04. Closure of the contacts |04 locks the relay 24 in the operated position and closure of contact 22 forms a link in the circuit from the power source 20 to the upper end of the operating coil I3.

Switch 'II is then closed to restore the meter relay 3| to neutral, after which switch 94 is closed to operate the relay 93, thereby substituting the impedance element |I for the element I0 in the branch 55 of the detector 32./In addition to the switch-over from one element to another the relay 93 opens the circuit at |20 and I 2| and closes the circuit at |22 and |23. Switch 'II is then opened to release the meter relay armature 69 which will move upward and close the circuit at 6l if the impedance of the element II is less than maximum. This applies operating current to the relay |30 through the contacts B1 and |22 and closes the contacts I3I and |32. Closure of the contact |32 locks the relay |30, and closure cf contact |3| completes the circuit from the power source 20 to the upper end of the operating coil I3, after which switch 2| is closed, thereby energizing the coil |3 and operating the acceptance device I4. The current path from the power source 20 to the operating coil I3 includes the switch |40, the contacts I3I and 22 and the switch 2|. The apparatus may be cleared for the next unit by momentarily closing switch '|I, momentarily opening switch I I I, and opening switch 34.

If the elements l0 and |I had an impedance higher than the predetermined maximum then the meter relay armature 00 would have operated downward and the relays 24 and |30 would have remained unenergized, leaving an open circuit between the power source 20 and the upper end of the operating coil I3. In this case the coil I3 could not be energized after the closure of switch 2|. l y

Although the detector `32 is responsive to impedance it is apparent that detectors responsive to other electrical characteristics could be substituted in the circuit without departing from the spirit and scope of the invention. The detector shown being responsive to impedance may also be used to detect components of impedance, such as, reactance and resistance, especially if a device under test is a substantially pure reactance or a substantially pure resistance. In cases of substantially pure reactances, the detector 32 may be set to detect capacitance or inductance.

It is to be understood that the above described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

l. An electrical testing apparatus comprising a detector for detecting electrical characteristics,

said detector having a first circuit closing means and a second circuit closing means, the first circuit closing means being responsive to detected values of the electrical characteristic below a predetermined value and the second circuit closing means being responsive to detected values above a predetermined value, a rst locking relay, a second locking relay, a third locking relay, switching means for selectively connecting the rst circuit closing means to either the first or the second relay thereby to make the first and the second relays individually responsive to the first circuit closing means when either is conected thereto. means for selectively connecting the second circuit closing means to either the third relay or an alternative circuit thereby to selectively make the third relay responsive to the second circuit closing means or to close said alternative circuit in response to the second circuit closing means, and an acceptance circuit operable in response to the contemporaneous operation of the rst, the second, and the third relays and the closing of the alternative circuit.

2. An electrical testing apparatus comprising a detector for comparing impedance devices under test with standard impedances, a plurality of standard impedances, means for selectively connecting either of said impedance standards to said detector, means for connecting an impedance device to be tested to said detector, means for substituting a second impedance device to be tested for the iirst device, said detector having a first circuit closing means responsive to predetermined impedance values of the device under test below a predetermined value and a second circuit closing means responsive to predetermined impedance values of the device under test above a predetermined value, a first locking relay operable in response to the first circuit closing means, a second locking relay operable in response to the second circuit closing means, a third locking relay, switching means for causing the third relay to operate in response to the first circuit closing means, switching means for causof the alternative circuit.

3. An electrical testing apparatus comprising a detector for comparing an electrical characteristicof devices under test with that of standard devices, a maximum standard device, a minimum standard device, means for selectively connecting either of said standard devices to said detector, means for connecting a device to be tested to said detector, means for substituting a second device to be tested for the first device to be tested, said detector having a rst and a second circuit closing means, the first circuit closing means being operable if the value of the electrical characteristic of the device under test is less than a predetermined maximum, the second circuit closing means being operable if the value of the electrical characteristic of the device under test is greater than a predetermined minimum, a. first locking relay operable in response to the first circuit closing means, a second locking relasr operable in response to the second circuit closing means, a third locking relay, switching means for causing the third relay to operate in response to the first circuit closing means, switching means for causing the second circuit closing means to close an alternative circuit instead of operating g the second relay, and an acceptance circuit operable in response to the contemporaneous operation of the first, second and third relays and the closure of the alternative circuit.

4. An electrical testing apparatus comprising an impedance detector having means for c'onnecting thereto an impedance device to be tested, a relay connected to said detector, said relay having a rst and a second circuit closing means, the rst circuit closing means being responsive through the detector to a test impedance connected to the detector having an' impedance value less than a predetermined maximum, the second circuit closing means being responsive through the detector to a test impedance connected to the detector having an impedance value greater than a predetermined minimum, a second relay operable in response to said nrst circuit closing means, a third'relay operable in response to said second circuit closing means, switching means for substituting a second impedance device to be tested in place of said rst impedance device being tested, a fourth relay operable in response to said rst circuit closing means when the second impedance device is substituted for the rst one by ancer device, said detector having a first and a. second circuit closing means, the rst circuit closing means being operable if the impedance value of the device under test is less than a predetermined maximum, the second circuit closing means being operable if the impedance value of the device under test is greater than a predetermined minimum, a first locking relay operable in response to the first circuit closing means, a secand locking relay operable in response to the second circuit closing means, a third locking relay, switching means for causing the third relay to operate in response to the rst circuit closing means, switching means for causing the second circuit closing means to close an alternative circuit instead of operating the second relay, and an acceptance circuit operable in response to the contemporaneous operation of the rst, second and third relays and the closure of the alternative circuit.

6. An electrical testing apparatus comprising an impedance detector for comparing impedance devices with standard impedances, a irst relay operable in response to changes in the detector caused by the device under test, said relay having alternative circuit closing means, means for connecting an impedance device to be tested to said detector, an impedance standard having diierent selectable values, means for connecting one value of the standard impedance to said detector for a first interval of time, a source of voltage, a second locking relay operable in response to operation of the first relay closing a rst alternative circuit, means operable after the rst interval of time for changing the value of the standard impedance in the .detector for a second interval of time, a third locking relay operable in response to operation of the first relay closing a second alternative circuit, means operable after the second time interval for making the rst relay operable to close either a third or a fourth alternative circuit, means operable after the second interval of time for substituting a second device to be tested for the first device under test, means operableF after the second time interval for .changing the value of the standard impedance in the detector for a third interval of time, a fourth locking relay operable in response to operation of the first relay closing the third alternative circuit, means operable after the third interval of time for changing the value of the standard impedance in the detector, and an acceptance device operable in response to voltage from said source transmitted to the acceptance device when the second, third and fourth relays are operated and the fourth alternative circuit is closed by the first relay.

. STEWART E. FRISBIE.

GILBERT E. WEEKS.

REFERENCES CITED l The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,983,388 Moore Dec. 4, 1934 2,153,990 Paulson Apr. 11, 1939 2,363,577 Dexter Nov. 28, 1944 2,417,488' Handforth et al. Mar. 18, 1947 

